Hekaton is Microsoft SQL Server's in-memory OLTP engine. It allows for creating memory-optimized tables to fully leverage RAM and provide faster performance than disk-based tables. Memory-optimized tables use new row formats and indexing structures like hash and range indexes that are optimized for memory. Stored procedures can be natively compiled for maximum speed when operating on memory-optimized tables. There are some limitations around data types and features supported. Diagnostic objects like DMVs provide visibility into Hekaton's memory usage and performance.